Forced through-flow steam generator having a superimposed forced circulation

ABSTRACT

An injection line is branched off from a point downstream of the circulating pump to inject water into a point between two of the superheaters. The flow rate in this line is measured and a corresponding signal is sent to a controller for regulating the amount of feed water delivered to the steam generator. This signal is superimposed on a signal of opposite sign derived from a measurement of the feed water rate downstream of the feed pump.

United States Patent [1 1 Laubli 1 Nov. 26, 1974 FORCED THROUGH-FLOW STEAM GENERATOR HAVING A SUPERIMPOSED FORCED CIRCULATION [75] Inventor: Fritz Laubli, Winterthur,

Switzerland [73] Assignee: Sulzer Brothers Ltd., Winterthur,

Switzerland [22] Filed: June 12, 1973 [21] Appl. No.: 369,193

[30] Foreign Application Priority Data June 12, 1972 Switzerland 8688/72 [52] US. Cl 122/479 S, 122/406 S [51] Int. Cl. F22g 5/12 [58] Field of Search 122/406 S, 406 ST, 448 S, 122/451 S, 479 S [56] References Cited UNITED STATES PATENTS 3,089,308 5/1963 Halle 122/451 X 3,134,367 5/1964 Halle 122/479 X 3,175,541 3/1965 Hottenstine 122/451 3,216,403 11/1965 Kolerup 122/451 Primary Examiner-Kenneth W. Sprague Attorney, Agent, or Firm-Kenyon & Kenyon Reilly Carr & Chapin [5 7] ABSTRACT An injection line is branched off from a point downstream of the circulating pump to inject water into a point between two of the superheaters. The flow rate in this line is measured and a corresponding signal is sent to a controller for regulating the amount of feed water delivered to the steam generator. This signal is superimposed on a signal of opposite sign derived from a measurement of the feed water rate downstream of the feed pump.

3 Claims, 2 Drawing Figures PATENTL, 51312 61874 SHEEI 2 OF 2 steam generator also has a circulation path comprising a line leading from the water separator to the main path upstream of the circulation pump; a water injection line leading from the main path between the circulation pump and the evaporator to an injection point in the main path between the superheaters and an injection valve in the injection line controlled in dependence on the temperature of the superheated steam as measured lation through the evaporator by means of at least one circulating pump, feed water being supplied to the suction side of the circulating pump. In this case, water obtained from the delivery of the circulating pump is injected into the superheated steam.

The term evaporator is defined in the above application as including the equivalent components in supercritical steam generators, usually afforded by the tubes of the combustion chamber walls, and the same definition is hereby adopted for the present specification. The reason for this definition is that the present invention is applicable to supercritical steam generators for which the term evaporator is not wholly appropriate.

An advantage of the method described in the above application is that the pressure drop across the evaporator is available for water injection so that an adequate pressure difference is available for injection even under conditions of part load. In the steam generator described in the above application, the rate of flow of feed water is controlled so as to tend to maintain a set value. However, disturbances can arise if a change in temperature in the superheated steam leads to an alteration in the injection flow rate. Such a disturbance can be corrected only slowly by the system described in that application. This is particularly serious if the rate of injection is controlled by a controller having integral action and the separator is operated under dry conditions. In this case, it is possible for the controller to change the rate of injection to the limit of the regulating range so that control is lost. Although'this could be avoided by employing a controller without any integral action, this is usually undesirable.

Accordingly, it is an object of the invention to control the feed water flow rate in a forced through-flow steam generator partly in dependence upon the rate of injection of water into the generated superheated steam.

It is another object of the invention to avoid changing the feed rate to an evaporator should a change in the injection rate occur.

It is another object of the invention to allow a rapid response to changes in temperature within a forced through-flow steam generator employing a controller having an integral action.

Briefly, the invention provides a forced throughflow steam generator having a superimposed circulation with a means of regulating the feed water flow in dependence on the delivered flow rate and an injection rate.

The steam generator includes a main working fluid path comprising, in series, a feed pump, a circulation pump, an evaporator (as herein defined), a water/- steam separator and at least two superheaters. The

by a suitable temperature measuring device.

The means for regulating the feed water flow includes a first device for measuring the flow delivered by the feed pump, a second device for measuring the flow in the water injection line and a controller for adjusting the feed water flow delivered by the feed pump in dependence upon the flow rate measured by the first device so as to tend to maintain thefeed water flow at a set value and in dependence upon the flow rate measured by the second device so as to tend to increase the feed water flow as the flow rate measured by the second device increases.

In a forced through-flow steam generator in accor dance with the present invention, the additional control on the feed water flow rate in dependence upon the rate of injection reduces, or avoids, the difficulty of correcting the injection rate should a change in temperature in the superheated steam occur.

The steam generator can be operated satisfactorily with the injection flow rate under the control of a controller having integral action. Best results are obtained when the controller is suplied with signals from the first device and the second device which are to the same scale. I

These and other objects and advantages of the invention will become more apparent from the following detailed description and appended claims taken in conjunction with the accompanying drawings in which:

FIG. l diagrammatically illustrates a steam generator according to the invention in which the injection flow rate at one injection point is used to control feed water flow rate; and

FIG. 2 diagrammatically illustrates a modified steam generator according to the invention in which the injection flow rate at two injection points is used to control the feed water flow rate.

Referring to FIG. 1, the forced through-flow steam generator includes a main working fluid path having a feed pump 1, a feed valve 2, a station 3 at which the feed water flow rate is measured by any suitable means, an economiser 4, a circulating pump 5, an evaporator 6, a water/steam separator 7, a superheater 8, an injection point 9, a superheater 10, an injection point 11, a final superheater l2 and a live steam line 13, all of which are connected in series in the order stated. A connecting line 20 forming a circulating path with a non-retum valve 21 leads from the separator 7 to a return point 22 which is located upstream of the circulating pump 5. An injection water duct 26 branches off from a point 25 upstream of the station 3 for measuring the feed water flow rate and leads via an injection valve 27 to the injection point 11. A temperature measuring sensor 28, whose output acts in a conventional manner on the injection valve 27 via a final temperature controller 29, is connected to the live steam line 13.

The water separator 7 is provided with a level measuring element 30, the output of which is connected to the left-hand input of a changeover switch 31. A temperature sensor 32 is provided at the downstream end of the first superheater 8 and has an output connected to the right-hand input of the changeover switch 31. The output of the changeover switch 31 acts via a controller 36 with proportional plus integral action as a set value on a feed controller 37. The feed controller 37 is also supplied with a measured value comprising the output of a measuring device or apparatus 38 for measuring the feed water flow rate at the station 3. The output of the feed controller 37 acts on the feed valve 2 in the sense that a rise in the measured feed water flow rate will tend to move the feed valve 2 in the closing direction and a rise of level in the water separator 7 or a reduction of temperature at the end of the superheater 8 will tend to move the feed valve 2 in the closing direction.

The feed regulator 37 is additionally connected via a conductor 40 to a load signal generator 41 which also supplies a load-dependent set value signal to the PI controller 36 via a conductor 42.

The load signal generator 41 also acts on a servomotor 34 which operates the changeover switch 31 by means of a rod 35, as is known, so that, at low loads, the switch 31 transmits the signal formed by the level measuring element 30 to the controller 36 but, at high loads, the switch 31 transmits the signal from the temperature sensor 32 to the controller 36. To this end, the load transmitter 41 is constructed so that the set value signal supplied to the controller 36 via the conductor 42 is simultaneously and suitably changed in the course or such a changeover operation. a

An injection line 50 branches off from the line joining the economiser 4 to the evaporator 6 at a point 55 which is downstream of the circulating pump 5. The injection line 50 rejoins the main working medium circuit at a point 9 between the first two superheaters 8 and 10 and contains a valve 51 which is conventionally actuated via a controller 53 with proportional plus integral action by a temperature measuring device 52 at the downstream end of the superheater 10. The injection line 50 contains a device 60 for measuring the flow rate of the injected water. The output of the flow rate measuring device 60 acts via a signal line 61 on the feed regulator 37 on the same scale but in the opposite sense a to the measured value signal of the means 38 for measuring the feed water flow rate.

The steam generator shown in FIG. 1 is suitable for sliding-pressure operation, the set value for the feed water "controller 37 being defined in the lower load range by the water level in the water separator 7, but in the upper load range in which the separator is operated dry by the temperature of the superheated steam measured at the end of the first superheater 8. While the injection point 11 is supplied with water in the conventional manner, the line 50 for the injection point 9 is branched off from the delivery of the circulating pump 5 so that a sufiiciently high injection pressure is ensured even at very low load. At high loads, when the circulating pump 5 is shut down, the pressure drop resulting from the increased flow rate across the evaporator 6 and the inlet superheater 8 is sufficient to provide an adequate injection pressure.

Influencing the feed controller 37 with a signalrepresenting the injected water flow rate measured in the injection line 50 ensures that any change of injected water flow rate immediately results in an equal change of feed water flow rate. Thus, the evaporator 6 is protected against any disturbance of the inlet flow rate.

Referring to FIG. 2, wherein like reference charac ters indicate like parts as above, the forced throughflow steam generator with superimposed circulation differs from that of FIG. 1 in that both injection points 9 and 11 are connected to the same injection line which is branched off at the point from the delivery of the circulating pump 5. In addition, the measured value supplied to the feed controller 37 is delivered by an integral-action controller 36' instead ofby a PI controller 36. This integral-action controller 36' is arranged to regulate the temperature difference measured by thermocouples which are disposed upstream and downstream of the injection point 11 as shown.

Supplying the feed regulator 37 with the output signal from the injected water flow measuring means in this embodiment also prevents the injection controller 53 from running off to the limit of the regulating range in the event of a change in the injected water flow rate and prevents any change of injected water flow rate from causing any disturbance in the feed rate to the evaporator.

What is claimed is:

1. A forced through-flow steam generator comprising a main working fluid path including, in series, a feed pump, a feed valve, a circulation pump, an evaporator, a water/steam separator and at least two superheaters;

a circulation path including a line extending from said separator to said main working fluid path upstream of said circulation pump;

a water injection line extending from said main working fluid path between'said circulation pump and said evaporator to an injection point in said main working fluid path between'said superheaters, and an injection valve in said line for controlling the flow therethrough in response to the temperature downstream of said superheaters; and

means for regulating the feed water flow including a firstdevice for measuring the flow delivered downstream of said feed pump, a second device for measuring the flow in said water injection line, and a controller connected to each said device and to said feed valve for adjusting the feed water flow from said feed pump in dependence upon the flow rate measured by said first device to tend to maintain the feed water flow at a set value and in dependence upon the flow rate measured by said second device to tend to increase the feed water flow as the flow rate measured by said second device increases.

2. A forced through-flow steam generator as set forth in claim 1 which further includes a level measuring element connected to said separator for measuring the level of water therein and emitting a signal in response thereto, a temperature sensor downstream of the first of said superheaters for measuring the temperature of steam therebetween and emitting a signal in response thereto, a proportional plus integral action controller selectively connected to one of said element and sensor to receive a signal therefrom, and a load transmitter connected to said latter controller to deliver a set value signal thereto for comparison with the received signal, said latter controller being connected to said first controller to deliver a set value thereto corresponding to the compared signals in said latter controller for comparison with signals received from said devices.

3. A method of controlling a forced through-flow steam generator having a main working fluid path including, in series, a feed pump, a feed valve, a circulation pump, an evaporator, a water/steam separator and at least two superheaters; a circulation path including a line extending from said separator to said main working fluid path upstream of said circulation pump; a water injection line extending from said main working fluid path between said circulation pump and said evaporator to an injection point in said main working fluid path between said superheaters, and an injection valve in said line for controlling the flow therethrough in response to the temperature downstream of said superheaters', and comprising the steps of measuring the flow delivered by said feed pump; measuring the flow in said water injection line; and

increases. 

1. A forced through-flow steam generator comprising a main working fluid path including, in series, a feed pump, a feed valve, a circulation pump, an evaporator, a water/steam separator and at least two superheaters; a circulation path including a line extending from said separator to said main working fluid path upstream of said circulation pump; a water injection line extending from said main working fluid path between said circulation pump and said evaporator to an injection point in said main working fluid path between said superheaters, and an injection valve in said line for controlling the flow therethrough in response to the temperature downstream of said superheaters; and means for regulating the feed water flow including a first device for measuring the flow delivered downstream of said feed pump, a second device for measuring the flow in said water injection line, and a controller connected to each said device and to said feed valve for adjusting the feed water flow from said feed pump in dependence upon the flow rate measured by said first device to tend to maintain the feed water flow at a set value and in dependence upon the flow rate measured by said second device to tend to increase the feed water flow as the flow rate measured by said second device increases.
 2. A forced through-flow steam generator as set forth in claim 1 which further includes a level measuring element connected to said separator for measuring the level of water therein and emitting a signal in response thereto, a temperature sensor downstream of the first of said superheaters for measuring the temperature of steam therebetween and emitting a signal in response thereto, a proportional plus integral action controller selectively connected to one of said element and sensor to receive a signal therefrom, and a load transmitter connected to said latter controller to deliver a set value signal thereto for comparison with the received signal; said latter controller being connected to said first controller to deliver a set value thereto corresponding to the compared signals in said latter controller for comparison with signals received from said devices.
 3. A method of controlling a forced through-flow steam generator having a main working fluid path including, in series, a feed pump, a feed valve, a circulation pump, an evaporator, a water/steam separator and at least two superheaters; a circulation path including a line extending from said separator to said main working fluid path upstream of said circulation pump; a water injection line extending from said main working fluid path between said circulation pump and said evaporator to an injection point in said main working fluid path between said superheaters, and an injection valve in said line for controlling the flow therethrough in response to the temperature downstream of said superheaters; and comprising the steps of measuring the flow delivered by said feed pump; measuring the flow in said water injection line; and adjusting the flow delivered by said feed pump in dependence upon the flow delivered by said feed pump to tend to maintain the feed water flow at a set value and in dependence upon the flow in said water injection line to tend to increase the feed water flow as the flow in said water injection line increases. 